1. Field of the Invention
This invention relates to a method of transmitting contents information. Also, this invention relates to a method of recording contents information. In addition, this invention relates to an apparatus for transmitting contents information. Furthermore, this invention relates to an apparatus for recording contents information. Also, this invention relates to a transmission medium. In addition, this invention relates to a recording medium. Furthermore, this invention relates to a method of decrypting contents information. Also, this invention relates to an apparatus for decrypting contents information.
2. Description of the Related Art
Japanese published unexamined patent application 10-269289 discloses a system for managing the distribution of digital contents. In the system of Japanese application 10-269289, a distributor side encrypts and compresses digital contents into processing-resultant digital contents. The distributor side transmits the processing-resultant digital contents, an encryption-resultant contents key, and encryption-resultant accounting information to a communication opposite party. The distributor side implements a process of receiving a charge on the basis of contents use information transmitted from the communication opposite party. Then, the distributor side implements a process of dividing the received charge among interested persons including a copyright holder of the digital contents. On the other hand, a user side (a digital contents player) decrypts and expands the processing-resultant digital contents in response to the contents key, thereby reproducing the original digital contents. The user side subjects the accounting information to a reducing process responsive to the use of the digital contents. The user side transmits the reduced accounting information and the contents use information to the distributor side.
Japanese published unexamined patent application 10-283268 discloses a system in which a recording medium stores encryption-resultant main information, and also encryption-resultant information representing a key for decrypting the encryption-resultant main information. Non-encrypted information representing conditions of decrypting the encryption-resultant main information is added to the encryption-resultant key information. In more detail, the encryption-resultant key information has non-encrypted control information which contains device information and region information. The control information is designed to prevent the encryption-resultant main information from being copied onto a magnetic recording medium or an optical disc in a user side for illegal use thereof.
Generally, typical cryptosystems (encryption-decryption systems) are of a symmetric type and an asymmetric type. In the symmetric cryptosystem, a common key is used by both an encryption side and a decryption side. On the other hand, the asymmetric cryptosystem uses a public key and a secret key. The symmetric cryptosystem is better than the asymmetric cryptosystem in data processing rate.
In a known hybrid cryptosystem, an encryption side encrypts contents information in response to a contents key according to a symmetric cryptography, and transmits the encryption-resultant contents information to a decryption side. In addition, the encryption side encrypts the contents key according to an asymmetric cryptography, and transmits the encryption-resultant contents key to the decryption side.
It is known to set a common master key in both an encryption side and a decryption side. In this case, an encryption side encrypts a contents key in response to the master key according to a symmetric cryptography, and transmits the encryption-resultant contents key to the decryption side.
In a prior-art symmetric cryptosystem using a contents key and a master key, both an encryption side and a decryption side know cryptographic algorithms providing a cryptographic relation among a master key, a contents key, and contents information. Accordingly, it is possible to make an imitation of the decryption side, that is, an illegal machine of the decryption side, only from knowledge of the encryption side.